Memory Transference

[KageTokage]

Alchemist 50-60 questline also involved transferring consciousness between bodies. It's apparently something the alchemists of Radz-at-Han can do, although it's also stated to be a nearly-impossible technique available only to the most skilled and least ethical of alchemists.

I forgot about that particular quest since it's been so terribly long.

It seemed more like a proper soul transfer as opposed to simply overriding someone else's memories, though, as the "color" of the offending alchemist's soul (Which is another concept that ended up coming back much later in Shadowbringers) matched that of the body he overtook.

[DemiurgeFerikad]

The Black Mage 60-70 quests also had an instance of memory transference. The Mhachi mage who first came up with Black Magic set up a spell that transferred a copy of her consciousness into one of our quest-line friends, and would occasionally take her over now and again. If I remember correctly, it started out as amnesia for the possessee, but she eventually started becoming cognizant of what was going on when she wasn't in control of her body.
It was only meant to last a short amount of time, and the transference wasn't permanent. But preserving and implanting new memories, or even entire personas, can be accomplished with a simple application of magic.